These are sites that have degraded into ruins.  I usually consider a structure to be in ruins if it is missing the majority of its roof.

Bannerman Castle, Hudson River, NY

Franny Reese State Park, Highland, NY

Cornish Estate (Northgate), Cold Spring, NY

Ruins at Arden Point, Garrison, NY

Manitou Point Preserve, Garrison, NY

Abandoned Barn, Noxon Road, LaGrange, NY

Rock Brook Ruins, Acadia, ME

Ruins at Lime Kiln Road, East Fishkill, NY

Ruins on Maloney Road, Wappinger, NY

St. Andrews Novitiate Agricultural Property, Hyde Park, NY

Former Mule Barn & Church, Kingston, NY

Overlook Mountain House, Woodstock, NY

Sutro Baths, San Francisco, CA

Bodie State Historic Park, Bodie, CA

Barge, Hyde Park, NY

Catskill Mountain House, Catskills, NY

Kaaterskill Hotel, Catskills, NY

Saw Mill & Kaaterskill Hotel Laundry Building, Catskill, NY

Sleightsburgh Spit Barge Graveyard, Port Ewen, NY

Brigham Brick Yard, Kingston, NY

Ruins and Dam, Poughkeepsie, NY

Ruins in Minnewaska State Park, Kerhonkson, NY

Denning’s Point Ruins, Beacon, NY

Palen Road Ruins, East Fishkill, NY

Love Road, Poughkeepsie, NY